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llvm-mirror/lib/Transforms/IPO/FunctionAttrs.cpp
Reid Kleckner 68092989f3 Sink all InitializePasses.h includes 
This file lists every pass in LLVM, and is included by Pass.h, which is
very popular. Every time we add, remove, or rename a pass in LLVM, it
caused lots of recompilation.

I found this fact by looking at this table, which is sorted by the
number of times a file was changed over the last 100,000 git commits
multiplied by the number of object files that depend on it in the
current checkout:
  recompiles    touches affected_files  header
  342380        95      3604    llvm/include/llvm/ADT/STLExtras.h
  314730        234     1345    llvm/include/llvm/InitializePasses.h
  307036        118     2602    llvm/include/llvm/ADT/APInt.h
  213049        59      3611    llvm/include/llvm/Support/MathExtras.h
  170422        47      3626    llvm/include/llvm/Support/Compiler.h
  162225        45      3605    llvm/include/llvm/ADT/Optional.h
  158319        63      2513    llvm/include/llvm/ADT/Triple.h
  140322        39      3598    llvm/include/llvm/ADT/StringRef.h
  137647        59      2333    llvm/include/llvm/Support/Error.h
  131619        73      1803    llvm/include/llvm/Support/FileSystem.h

Before this change, touching InitializePasses.h would cause 1345 files
to recompile. After this change, touching it only causes 550 compiles in
an incremental rebuild.

Reviewers: bkramer, asbirlea, bollu, jdoerfert

Differential Revision: https://reviews.llvm.org/D70211
2019-11-13 16:34:37 -08:00

1631 lines
55 KiB
C++
Raw Blame History

//===- FunctionAttrs.cpp - Pass which marks functions attributes ----------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
/// \file
/// This file implements interprocedural passes which walk the
/// call-graph deducing and/or propagating function attributes.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/IPO/FunctionAttrs.h"
#include "llvm/ADT/SCCIterator.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/BasicAliasAnalysis.h"
#include "llvm/Analysis/CGSCCPassManager.h"
#include "llvm/Analysis/CallGraph.h"
#include "llvm/Analysis/CallGraphSCCPass.h"
#include "llvm/Analysis/CaptureTracking.h"
#include "llvm/Analysis/LazyCallGraph.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/MemoryLocation.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Argument.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Use.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/IPO.h"
#include <cassert>
#include <iterator>
#include <map>
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "functionattrs"
STATISTIC(NumReadNone, "Number of functions marked readnone");
STATISTIC(NumReadOnly, "Number of functions marked readonly");
STATISTIC(NumWriteOnly, "Number of functions marked writeonly");
STATISTIC(NumNoCapture, "Number of arguments marked nocapture");
STATISTIC(NumReturned, "Number of arguments marked returned");
STATISTIC(NumReadNoneArg, "Number of arguments marked readnone");
STATISTIC(NumReadOnlyArg, "Number of arguments marked readonly");
STATISTIC(NumNoAlias, "Number of function returns marked noalias");
STATISTIC(NumNonNullReturn, "Number of function returns marked nonnull");
STATISTIC(NumNoRecurse, "Number of functions marked as norecurse");
STATISTIC(NumNoUnwind, "Number of functions marked as nounwind");
STATISTIC(NumNoFree, "Number of functions marked as nofree");
static cl::opt<bool> EnableNonnullArgPropagation(
"enable-nonnull-arg-prop", cl::init(true), cl::Hidden,
cl::desc("Try to propagate nonnull argument attributes from callsites to "
"caller functions."));
static cl::opt<bool> DisableNoUnwindInference(
"disable-nounwind-inference", cl::Hidden,
cl::desc("Stop inferring nounwind attribute during function-attrs pass"));
static cl::opt<bool> DisableNoFreeInference(
"disable-nofree-inference", cl::Hidden,
cl::desc("Stop inferring nofree attribute during function-attrs pass"));
namespace {
using SCCNodeSet = SmallSetVector<Function *, 8>;
} // end anonymous namespace
/// Returns the memory access attribute for function F using AAR for AA results,
/// where SCCNodes is the current SCC.
///
/// If ThisBody is true, this function may examine the function body and will
/// return a result pertaining to this copy of the function. If it is false, the
/// result will be based only on AA results for the function declaration; it
/// will be assumed that some other (perhaps less optimized) version of the
/// function may be selected at link time.
static MemoryAccessKind checkFunctionMemoryAccess(Function &F, bool ThisBody,
AAResults &AAR,
const SCCNodeSet &SCCNodes) {
FunctionModRefBehavior MRB = AAR.getModRefBehavior(&F);
if (MRB == FMRB_DoesNotAccessMemory)
// Already perfect!
return MAK_ReadNone;
if (!ThisBody) {
if (AliasAnalysis::onlyReadsMemory(MRB))
return MAK_ReadOnly;
if (AliasAnalysis::doesNotReadMemory(MRB))
return MAK_WriteOnly;
// Conservatively assume it reads and writes to memory.
return MAK_MayWrite;
}
// Scan the function body for instructions that may read or write memory.
bool ReadsMemory = false;
bool WritesMemory = false;
for (inst_iterator II = inst_begin(F), E = inst_end(F); II != E; ++II) {
Instruction *I = &*II;
// Some instructions can be ignored even if they read or write memory.
// Detect these now, skipping to the next instruction if one is found.
if (auto *Call = dyn_cast<CallBase>(I)) {
// Ignore calls to functions in the same SCC, as long as the call sites
// don't have operand bundles. Calls with operand bundles are allowed to
// have memory effects not described by the memory effects of the call
// target.
if (!Call->hasOperandBundles() && Call->getCalledFunction() &&
SCCNodes.count(Call->getCalledFunction()))
continue;
FunctionModRefBehavior MRB = AAR.getModRefBehavior(Call);
ModRefInfo MRI = createModRefInfo(MRB);
// If the call doesn't access memory, we're done.
if (isNoModRef(MRI))
continue;
if (!AliasAnalysis::onlyAccessesArgPointees(MRB)) {
// The call could access any memory. If that includes writes, note it.
if (isModSet(MRI))
WritesMemory = true;
// If it reads, note it.
if (isRefSet(MRI))
ReadsMemory = true;
continue;
}
// Check whether all pointer arguments point to local memory, and
// ignore calls that only access local memory.
for (CallSite::arg_iterator CI = Call->arg_begin(), CE = Call->arg_end();
CI != CE; ++CI) {
Value *Arg = *CI;
if (!Arg->getType()->isPtrOrPtrVectorTy())
continue;
AAMDNodes AAInfo;
I->getAAMetadata(AAInfo);
MemoryLocation Loc(Arg, LocationSize::unknown(), AAInfo);
// Skip accesses to local or constant memory as they don't impact the
// externally visible mod/ref behavior.
if (AAR.pointsToConstantMemory(Loc, /*OrLocal=*/true))
continue;
if (isModSet(MRI))
// Writes non-local memory.
WritesMemory = true;
if (isRefSet(MRI))
// Ok, it reads non-local memory.
ReadsMemory = true;
}
continue;
} else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
// Ignore non-volatile loads from local memory. (Atomic is okay here.)
if (!LI->isVolatile()) {
MemoryLocation Loc = MemoryLocation::get(LI);
if (AAR.pointsToConstantMemory(Loc, /*OrLocal=*/true))
continue;
}
} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
// Ignore non-volatile stores to local memory. (Atomic is okay here.)
if (!SI->isVolatile()) {
MemoryLocation Loc = MemoryLocation::get(SI);
if (AAR.pointsToConstantMemory(Loc, /*OrLocal=*/true))
continue;
}
} else if (VAArgInst *VI = dyn_cast<VAArgInst>(I)) {
// Ignore vaargs on local memory.
MemoryLocation Loc = MemoryLocation::get(VI);
if (AAR.pointsToConstantMemory(Loc, /*OrLocal=*/true))
continue;
}
// Any remaining instructions need to be taken seriously! Check if they
// read or write memory.
//
// Writes memory, remember that.
WritesMemory |= I->mayWriteToMemory();
// If this instruction may read memory, remember that.
ReadsMemory |= I->mayReadFromMemory();
}
if (WritesMemory) {
if (!ReadsMemory)
return MAK_WriteOnly;
else
return MAK_MayWrite;
}
return ReadsMemory ? MAK_ReadOnly : MAK_ReadNone;
}
MemoryAccessKind llvm::computeFunctionBodyMemoryAccess(Function &F,
AAResults &AAR) {
return checkFunctionMemoryAccess(F, /*ThisBody=*/true, AAR, {});
}
/// Deduce readonly/readnone attributes for the SCC.
template <typename AARGetterT>
static bool addReadAttrs(const SCCNodeSet &SCCNodes, AARGetterT &&AARGetter) {
// Check if any of the functions in the SCC read or write memory. If they
// write memory then they can't be marked readnone or readonly.
bool ReadsMemory = false;
bool WritesMemory = false;
for (Function *F : SCCNodes) {
// Call the callable parameter to look up AA results for this function.
AAResults &AAR = AARGetter(*F);
// Non-exact function definitions may not be selected at link time, and an
// alternative version that writes to memory may be selected. See the
// comment on GlobalValue::isDefinitionExact for more details.
switch (checkFunctionMemoryAccess(*F, F->hasExactDefinition(),
AAR, SCCNodes)) {
case MAK_MayWrite:
return false;
case MAK_ReadOnly:
ReadsMemory = true;
break;
case MAK_WriteOnly:
WritesMemory = true;
break;
case MAK_ReadNone:
// Nothing to do!
break;
}
}
// If the SCC contains both functions that read and functions that write, then
// we cannot add readonly attributes.
if (ReadsMemory && WritesMemory)
return false;
// Success! Functions in this SCC do not access memory, or only read memory.
// Give them the appropriate attribute.
bool MadeChange = false;
for (Function *F : SCCNodes) {
if (F->doesNotAccessMemory())
// Already perfect!
continue;
if (F->onlyReadsMemory() && ReadsMemory)
// No change.
continue;
if (F->doesNotReadMemory() && WritesMemory)
continue;
MadeChange = true;
// Clear out any existing attributes.
F->removeFnAttr(Attribute::ReadOnly);
F->removeFnAttr(Attribute::ReadNone);
F->removeFnAttr(Attribute::WriteOnly);
if (!WritesMemory && !ReadsMemory) {
// Clear out any "access range attributes" if readnone was deduced.
F->removeFnAttr(Attribute::ArgMemOnly);
F->removeFnAttr(Attribute::InaccessibleMemOnly);
F->removeFnAttr(Attribute::InaccessibleMemOrArgMemOnly);
}
// Add in the new attribute.
if (WritesMemory && !ReadsMemory)
F->addFnAttr(Attribute::WriteOnly);
else
F->addFnAttr(ReadsMemory ? Attribute::ReadOnly : Attribute::ReadNone);
if (WritesMemory && !ReadsMemory)
++NumWriteOnly;
else if (ReadsMemory)
++NumReadOnly;
else
++NumReadNone;
}
return MadeChange;
}
namespace {
/// For a given pointer Argument, this retains a list of Arguments of functions
/// in the same SCC that the pointer data flows into. We use this to build an
/// SCC of the arguments.
struct ArgumentGraphNode {
Argument *Definition;
SmallVector<ArgumentGraphNode *, 4> Uses;
};
class ArgumentGraph {
// We store pointers to ArgumentGraphNode objects, so it's important that
// that they not move around upon insert.
using ArgumentMapTy = std::map<Argument *, ArgumentGraphNode>;
ArgumentMapTy ArgumentMap;
// There is no root node for the argument graph, in fact:
// void f(int *x, int *y) { if (...) f(x, y); }
// is an example where the graph is disconnected. The SCCIterator requires a
// single entry point, so we maintain a fake ("synthetic") root node that
// uses every node. Because the graph is directed and nothing points into
// the root, it will not participate in any SCCs (except for its own).
ArgumentGraphNode SyntheticRoot;
public:
ArgumentGraph() { SyntheticRoot.Definition = nullptr; }
using iterator = SmallVectorImpl<ArgumentGraphNode *>::iterator;
iterator begin() { return SyntheticRoot.Uses.begin(); }
iterator end() { return SyntheticRoot.Uses.end(); }
ArgumentGraphNode *getEntryNode() { return &SyntheticRoot; }
ArgumentGraphNode *operator[](Argument *A) {
ArgumentGraphNode &Node = ArgumentMap[A];
Node.Definition = A;
SyntheticRoot.Uses.push_back(&Node);
return &Node;
}
};
/// This tracker checks whether callees are in the SCC, and if so it does not
/// consider that a capture, instead adding it to the "Uses" list and
/// continuing with the analysis.
struct ArgumentUsesTracker : public CaptureTracker {
ArgumentUsesTracker(const SCCNodeSet &SCCNodes) : SCCNodes(SCCNodes) {}
void tooManyUses() override { Captured = true; }
bool captured(const Use *U) override {
CallSite CS(U->getUser());
if (!CS.getInstruction()) {
Captured = true;
return true;
}
Function *F = CS.getCalledFunction();
if (!F || !F->hasExactDefinition() || !SCCNodes.count(F)) {
Captured = true;
return true;
}
// Note: the callee and the two successor blocks *follow* the argument
// operands. This means there is no need to adjust UseIndex to account for
// these.
unsigned UseIndex =
std::distance(const_cast<const Use *>(CS.arg_begin()), U);
assert(UseIndex < CS.data_operands_size() &&
"Indirect function calls should have been filtered above!");
if (UseIndex >= CS.getNumArgOperands()) {
// Data operand, but not a argument operand -- must be a bundle operand
assert(CS.hasOperandBundles() && "Must be!");
// CaptureTracking told us that we're being captured by an operand bundle
// use. In this case it does not matter if the callee is within our SCC
// or not -- we've been captured in some unknown way, and we have to be
// conservative.
Captured = true;
return true;
}
if (UseIndex >= F->arg_size()) {
assert(F->isVarArg() && "More params than args in non-varargs call");
Captured = true;
return true;
}
Uses.push_back(&*std::next(F->arg_begin(), UseIndex));
return false;
}
// True only if certainly captured (used outside our SCC).
bool Captured = false;
// Uses within our SCC.
SmallVector<Argument *, 4> Uses;
const SCCNodeSet &SCCNodes;
};
} // end anonymous namespace
namespace llvm {
template <> struct GraphTraits<ArgumentGraphNode *> {
using NodeRef = ArgumentGraphNode *;
using ChildIteratorType = SmallVectorImpl<ArgumentGraphNode *>::iterator;
static NodeRef getEntryNode(NodeRef A) { return A; }
static ChildIteratorType child_begin(NodeRef N) { return N->Uses.begin(); }
static ChildIteratorType child_end(NodeRef N) { return N->Uses.end(); }
};
template <>
struct GraphTraits<ArgumentGraph *> : public GraphTraits<ArgumentGraphNode *> {
static NodeRef getEntryNode(ArgumentGraph *AG) { return AG->getEntryNode(); }
static ChildIteratorType nodes_begin(ArgumentGraph *AG) {
return AG->begin();
}
static ChildIteratorType nodes_end(ArgumentGraph *AG) { return AG->end(); }
};
} // end namespace llvm
/// Returns Attribute::None, Attribute::ReadOnly or Attribute::ReadNone.
static Attribute::AttrKind
determinePointerReadAttrs(Argument *A,
const SmallPtrSet<Argument *, 8> &SCCNodes) {
SmallVector<Use *, 32> Worklist;
SmallPtrSet<Use *, 32> Visited;
// inalloca arguments are always clobbered by the call.
if (A->hasInAllocaAttr())
return Attribute::None;
bool IsRead = false;
// We don't need to track IsWritten. If A is written to, return immediately.
for (Use &U : A->uses()) {
Visited.insert(&U);
Worklist.push_back(&U);
}
while (!Worklist.empty()) {
Use *U = Worklist.pop_back_val();
Instruction *I = cast<Instruction>(U->getUser());
switch (I->getOpcode()) {
case Instruction::BitCast:
case Instruction::GetElementPtr:
case Instruction::PHI:
case Instruction::Select:
case Instruction::AddrSpaceCast:
// The original value is not read/written via this if the new value isn't.
for (Use &UU : I->uses())
if (Visited.insert(&UU).second)
Worklist.push_back(&UU);
break;
case Instruction::Call:
case Instruction::Invoke: {
bool Captures = true;
if (I->getType()->isVoidTy())
Captures = false;
auto AddUsersToWorklistIfCapturing = [&] {
if (Captures)
for (Use &UU : I->uses())
if (Visited.insert(&UU).second)
Worklist.push_back(&UU);
};
CallSite CS(I);
if (CS.doesNotAccessMemory()) {
AddUsersToWorklistIfCapturing();
continue;
}
Function *F = CS.getCalledFunction();
if (!F) {
if (CS.onlyReadsMemory()) {
IsRead = true;
AddUsersToWorklistIfCapturing();
continue;
}
return Attribute::None;
}
// Note: the callee and the two successor blocks *follow* the argument
// operands. This means there is no need to adjust UseIndex to account
// for these.
unsigned UseIndex = std::distance(CS.arg_begin(), U);
// U cannot be the callee operand use: since we're exploring the
// transitive uses of an Argument, having such a use be a callee would
// imply the CallSite is an indirect call or invoke; and we'd take the
// early exit above.
assert(UseIndex < CS.data_operands_size() &&
"Data operand use expected!");
bool IsOperandBundleUse = UseIndex >= CS.getNumArgOperands();
if (UseIndex >= F->arg_size() && !IsOperandBundleUse) {
assert(F->isVarArg() && "More params than args in non-varargs call");
return Attribute::None;
}
Captures &= !CS.doesNotCapture(UseIndex);
// Since the optimizer (by design) cannot see the data flow corresponding
// to a operand bundle use, these cannot participate in the optimistic SCC
// analysis. Instead, we model the operand bundle uses as arguments in
// call to a function external to the SCC.
if (IsOperandBundleUse ||
!SCCNodes.count(&*std::next(F->arg_begin(), UseIndex))) {
// The accessors used on CallSite here do the right thing for calls and
// invokes with operand bundles.
if (!CS.onlyReadsMemory() && !CS.onlyReadsMemory(UseIndex))
return Attribute::None;
if (!CS.doesNotAccessMemory(UseIndex))
IsRead = true;
}
AddUsersToWorklistIfCapturing();
break;
}
case Instruction::Load:
// A volatile load has side effects beyond what readonly can be relied
// upon.
if (cast<LoadInst>(I)->isVolatile())
return Attribute::None;
IsRead = true;
break;
case Instruction::ICmp:
case Instruction::Ret:
break;
default:
return Attribute::None;
}
}
return IsRead ? Attribute::ReadOnly : Attribute::ReadNone;
}
/// Deduce returned attributes for the SCC.
static bool addArgumentReturnedAttrs(const SCCNodeSet &SCCNodes) {
bool Changed = false;
// Check each function in turn, determining if an argument is always returned.
for (Function *F : SCCNodes) {
// We can infer and propagate function attributes only when we know that the
// definition we'll get at link time is *exactly* the definition we see now.
// For more details, see GlobalValue::mayBeDerefined.
if (!F->hasExactDefinition())
continue;
if (F->getReturnType()->isVoidTy())
continue;
// There is nothing to do if an argument is already marked as 'returned'.
if (llvm::any_of(F->args(),
[](const Argument &Arg) { return Arg.hasReturnedAttr(); }))
continue;
auto FindRetArg = [&]() -> Value * {
Value *RetArg = nullptr;
for (BasicBlock &BB : *F)
if (auto *Ret = dyn_cast<ReturnInst>(BB.getTerminator())) {
// Note that stripPointerCasts should look through functions with
// returned arguments.
Value *RetVal = Ret->getReturnValue()->stripPointerCasts();
if (!isa<Argument>(RetVal) || RetVal->getType() != F->getReturnType())
return nullptr;
if (!RetArg)
RetArg = RetVal;
else if (RetArg != RetVal)
return nullptr;
}
return RetArg;
};
if (Value *RetArg = FindRetArg()) {
auto *A = cast<Argument>(RetArg);
A->addAttr(Attribute::Returned);
++NumReturned;
Changed = true;
}
}
return Changed;
}
/// If a callsite has arguments that are also arguments to the parent function,
/// try to propagate attributes from the callsite's arguments to the parent's
/// arguments. This may be important because inlining can cause information loss
/// when attribute knowledge disappears with the inlined call.
static bool addArgumentAttrsFromCallsites(Function &F) {
if (!EnableNonnullArgPropagation)
return false;
bool Changed = false;
// For an argument attribute to transfer from a callsite to the parent, the
// call must be guaranteed to execute every time the parent is called.
// Conservatively, just check for calls in the entry block that are guaranteed
// to execute.
// TODO: This could be enhanced by testing if the callsite post-dominates the
// entry block or by doing simple forward walks or backward walks to the
// callsite.
BasicBlock &Entry = F.getEntryBlock();
for (Instruction &I : Entry) {
if (auto CS = CallSite(&I)) {
if (auto *CalledFunc = CS.getCalledFunction()) {
for (auto &CSArg : CalledFunc->args()) {
if (!CSArg.hasNonNullAttr())
continue;
// If the non-null callsite argument operand is an argument to 'F'
// (the caller) and the call is guaranteed to execute, then the value
// must be non-null throughout 'F'.
auto *FArg = dyn_cast<Argument>(CS.getArgOperand(CSArg.getArgNo()));
if (FArg && !FArg->hasNonNullAttr()) {
FArg->addAttr(Attribute::NonNull);
Changed = true;
}
}
}
}
if (!isGuaranteedToTransferExecutionToSuccessor(&I))
break;
}
return Changed;
}
static bool addReadAttr(Argument *A, Attribute::AttrKind R) {
assert((R == Attribute::ReadOnly || R == Attribute::ReadNone)
&& "Must be a Read attribute.");
assert(A && "Argument must not be null.");
// If the argument already has the attribute, nothing needs to be done.
if (A->hasAttribute(R))
return false;
// Otherwise, remove potentially conflicting attribute, add the new one,
// and update statistics.
A->removeAttr(Attribute::WriteOnly);
A->removeAttr(Attribute::ReadOnly);
A->removeAttr(Attribute::ReadNone);
A->addAttr(R);
R == Attribute::ReadOnly ? ++NumReadOnlyArg : ++NumReadNoneArg;
return true;
}
/// Deduce nocapture attributes for the SCC.
static bool addArgumentAttrs(const SCCNodeSet &SCCNodes) {
bool Changed = false;
ArgumentGraph AG;
// Check each function in turn, determining which pointer arguments are not
// captured.
for (Function *F : SCCNodes) {
// We can infer and propagate function attributes only when we know that the
// definition we'll get at link time is *exactly* the definition we see now.
// For more details, see GlobalValue::mayBeDerefined.
if (!F->hasExactDefinition())
continue;
Changed |= addArgumentAttrsFromCallsites(*F);
// Functions that are readonly (or readnone) and nounwind and don't return
// a value can't capture arguments. Don't analyze them.
if (F->onlyReadsMemory() && F->doesNotThrow() &&
F->getReturnType()->isVoidTy()) {
for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end(); A != E;
++A) {
if (A->getType()->isPointerTy() && !A->hasNoCaptureAttr()) {
A->addAttr(Attribute::NoCapture);
++NumNoCapture;
Changed = true;
}
}
continue;
}
for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end(); A != E;
++A) {
if (!A->getType()->isPointerTy())
continue;
bool HasNonLocalUses = false;
if (!A->hasNoCaptureAttr()) {
ArgumentUsesTracker Tracker(SCCNodes);
PointerMayBeCaptured(&*A, &Tracker);
if (!Tracker.Captured) {
if (Tracker.Uses.empty()) {
// If it's trivially not captured, mark it nocapture now.
A->addAttr(Attribute::NoCapture);
++NumNoCapture;
Changed = true;
} else {
// If it's not trivially captured and not trivially not captured,
// then it must be calling into another function in our SCC. Save
// its particulars for Argument-SCC analysis later.
ArgumentGraphNode *Node = AG[&*A];
for (Argument *Use : Tracker.Uses) {
Node->Uses.push_back(AG[Use]);
if (Use != &*A)
HasNonLocalUses = true;
}
}
}
// Otherwise, it's captured. Don't bother doing SCC analysis on it.
}
if (!HasNonLocalUses && !A->onlyReadsMemory()) {
// Can we determine that it's readonly/readnone without doing an SCC?
// Note that we don't allow any calls at all here, or else our result
// will be dependent on the iteration order through the functions in the
// SCC.
SmallPtrSet<Argument *, 8> Self;
Self.insert(&*A);
Attribute::AttrKind R = determinePointerReadAttrs(&*A, Self);
if (R != Attribute::None)
Changed = addReadAttr(A, R);
}
}
}
// The graph we've collected is partial because we stopped scanning for
// argument uses once we solved the argument trivially. These partial nodes
// show up as ArgumentGraphNode objects with an empty Uses list, and for
// these nodes the final decision about whether they capture has already been
// made. If the definition doesn't have a 'nocapture' attribute by now, it
// captures.
for (scc_iterator<ArgumentGraph *> I = scc_begin(&AG); !I.isAtEnd(); ++I) {
const std::vector<ArgumentGraphNode *> &ArgumentSCC = *I;
if (ArgumentSCC.size() == 1) {
if (!ArgumentSCC[0]->Definition)
continue; // synthetic root node
// eg. "void f(int* x) { if (...) f(x); }"
if (ArgumentSCC[0]->Uses.size() == 1 &&
ArgumentSCC[0]->Uses[0] == ArgumentSCC[0]) {
Argument *A = ArgumentSCC[0]->Definition;
A->addAttr(Attribute::NoCapture);
++NumNoCapture;
Changed = true;
}
continue;
}
bool SCCCaptured = false;
for (auto I = ArgumentSCC.begin(), E = ArgumentSCC.end();
I != E && !SCCCaptured; ++I) {
ArgumentGraphNode *Node = *I;
if (Node->Uses.empty()) {
if (!Node->Definition->hasNoCaptureAttr())
SCCCaptured = true;
}
}
if (SCCCaptured)
continue;
SmallPtrSet<Argument *, 8> ArgumentSCCNodes;
// Fill ArgumentSCCNodes with the elements of the ArgumentSCC. Used for
// quickly looking up whether a given Argument is in this ArgumentSCC.
for (ArgumentGraphNode *I : ArgumentSCC) {
ArgumentSCCNodes.insert(I->Definition);
}
for (auto I = ArgumentSCC.begin(), E = ArgumentSCC.end();
I != E && !SCCCaptured; ++I) {
ArgumentGraphNode *N = *I;
for (ArgumentGraphNode *Use : N->Uses) {
Argument *A = Use->Definition;
if (A->hasNoCaptureAttr() || ArgumentSCCNodes.count(A))
continue;
SCCCaptured = true;
break;
}
}
if (SCCCaptured)
continue;
for (unsigned i = 0, e = ArgumentSCC.size(); i != e; ++i) {
Argument *A = ArgumentSCC[i]->Definition;
A->addAttr(Attribute::NoCapture);
++NumNoCapture;
Changed = true;
}
// We also want to compute readonly/readnone. With a small number of false
// negatives, we can assume that any pointer which is captured isn't going
// to be provably readonly or readnone, since by definition we can't
// analyze all uses of a captured pointer.
//
// The false negatives happen when the pointer is captured by a function
// that promises readonly/readnone behaviour on the pointer, then the
// pointer's lifetime ends before anything that writes to arbitrary memory.
// Also, a readonly/readnone pointer may be returned, but returning a
// pointer is capturing it.
Attribute::AttrKind ReadAttr = Attribute::ReadNone;
for (unsigned i = 0, e = ArgumentSCC.size(); i != e; ++i) {
Argument *A = ArgumentSCC[i]->Definition;
Attribute::AttrKind K = determinePointerReadAttrs(A, ArgumentSCCNodes);
if (K == Attribute::ReadNone)
continue;
if (K == Attribute::ReadOnly) {
ReadAttr = Attribute::ReadOnly;
continue;
}
ReadAttr = K;
break;
}
if (ReadAttr != Attribute::None) {
for (unsigned i = 0, e = ArgumentSCC.size(); i != e; ++i) {
Argument *A = ArgumentSCC[i]->Definition;
Changed = addReadAttr(A, ReadAttr);
}
}
}
return Changed;
}
/// Tests whether a function is "malloc-like".
///
/// A function is "malloc-like" if it returns either null or a pointer that
/// doesn't alias any other pointer visible to the caller.
static bool isFunctionMallocLike(Function *F, const SCCNodeSet &SCCNodes) {
SmallSetVector<Value *, 8> FlowsToReturn;
for (BasicBlock &BB : *F)
if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB.getTerminator()))
FlowsToReturn.insert(Ret->getReturnValue());
for (unsigned i = 0; i != FlowsToReturn.size(); ++i) {
Value *RetVal = FlowsToReturn[i];
if (Constant *C = dyn_cast<Constant>(RetVal)) {
if (!C->isNullValue() && !isa<UndefValue>(C))
return false;
continue;
}
if (isa<Argument>(RetVal))
return false;
if (Instruction *RVI = dyn_cast<Instruction>(RetVal))
switch (RVI->getOpcode()) {
// Extend the analysis by looking upwards.
case Instruction::BitCast:
case Instruction::GetElementPtr:
case Instruction::AddrSpaceCast:
FlowsToReturn.insert(RVI->getOperand(0));
continue;
case Instruction::Select: {
SelectInst *SI = cast<SelectInst>(RVI);
FlowsToReturn.insert(SI->getTrueValue());
FlowsToReturn.insert(SI->getFalseValue());
continue;
}
case Instruction::PHI: {
PHINode *PN = cast<PHINode>(RVI);
for (Value *IncValue : PN->incoming_values())
FlowsToReturn.insert(IncValue);
continue;
}
// Check whether the pointer came from an allocation.
case Instruction::Alloca:
break;
case Instruction::Call:
case Instruction::Invoke: {
CallSite CS(RVI);
if (CS.hasRetAttr(Attribute::NoAlias))
break;
if (CS.getCalledFunction() && SCCNodes.count(CS.getCalledFunction()))
break;
LLVM_FALLTHROUGH;
}
default:
return false; // Did not come from an allocation.
}
if (PointerMayBeCaptured(RetVal, false, /*StoreCaptures=*/false))
return false;
}
return true;
}
/// Deduce noalias attributes for the SCC.
static bool addNoAliasAttrs(const SCCNodeSet &SCCNodes) {
// Check each function in turn, determining which functions return noalias
// pointers.
for (Function *F : SCCNodes) {
// Already noalias.
if (F->returnDoesNotAlias())
continue;
// We can infer and propagate function attributes only when we know that the
// definition we'll get at link time is *exactly* the definition we see now.
// For more details, see GlobalValue::mayBeDerefined.
if (!F->hasExactDefinition())
return false;
// We annotate noalias return values, which are only applicable to
// pointer types.
if (!F->getReturnType()->isPointerTy())
continue;
if (!isFunctionMallocLike(F, SCCNodes))
return false;
}
bool MadeChange = false;
for (Function *F : SCCNodes) {
if (F->returnDoesNotAlias() ||
!F->getReturnType()->isPointerTy())
continue;
F->setReturnDoesNotAlias();
++NumNoAlias;
MadeChange = true;
}
return MadeChange;
}
/// Tests whether this function is known to not return null.
///
/// Requires that the function returns a pointer.
///
/// Returns true if it believes the function will not return a null, and sets
/// \p Speculative based on whether the returned conclusion is a speculative
/// conclusion due to SCC calls.
static bool isReturnNonNull(Function *F, const SCCNodeSet &SCCNodes,
bool &Speculative) {
assert(F->getReturnType()->isPointerTy() &&
"nonnull only meaningful on pointer types");
Speculative = false;
SmallSetVector<Value *, 8> FlowsToReturn;
for (BasicBlock &BB : *F)
if (auto *Ret = dyn_cast<ReturnInst>(BB.getTerminator()))
FlowsToReturn.insert(Ret->getReturnValue());
auto &DL = F->getParent()->getDataLayout();
for (unsigned i = 0; i != FlowsToReturn.size(); ++i) {
Value *RetVal = FlowsToReturn[i];
// If this value is locally known to be non-null, we're good
if (isKnownNonZero(RetVal, DL))
continue;
// Otherwise, we need to look upwards since we can't make any local
// conclusions.
Instruction *RVI = dyn_cast<Instruction>(RetVal);
if (!RVI)
return false;
switch (RVI->getOpcode()) {
// Extend the analysis by looking upwards.
case Instruction::BitCast:
case Instruction::GetElementPtr:
case Instruction::AddrSpaceCast:
FlowsToReturn.insert(RVI->getOperand(0));
continue;
case Instruction::Select: {
SelectInst *SI = cast<SelectInst>(RVI);
FlowsToReturn.insert(SI->getTrueValue());
FlowsToReturn.insert(SI->getFalseValue());
continue;
}
case Instruction::PHI: {
PHINode *PN = cast<PHINode>(RVI);
for (int i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
FlowsToReturn.insert(PN->getIncomingValue(i));
continue;
}
case Instruction::Call:
case Instruction::Invoke: {
CallSite CS(RVI);
Function *Callee = CS.getCalledFunction();
// A call to a node within the SCC is assumed to return null until
// proven otherwise
if (Callee && SCCNodes.count(Callee)) {
Speculative = true;
continue;
}
return false;
}
default:
return false; // Unknown source, may be null
};
llvm_unreachable("should have either continued or returned");
}
return true;
}
/// Deduce nonnull attributes for the SCC.
static bool addNonNullAttrs(const SCCNodeSet &SCCNodes) {
// Speculative that all functions in the SCC return only nonnull
// pointers. We may refute this as we analyze functions.
bool SCCReturnsNonNull = true;
bool MadeChange = false;
// Check each function in turn, determining which functions return nonnull
// pointers.
for (Function *F : SCCNodes) {
// Already nonnull.
if (F->getAttributes().hasAttribute(AttributeList::ReturnIndex,
Attribute::NonNull))
continue;
// We can infer and propagate function attributes only when we know that the
// definition we'll get at link time is *exactly* the definition we see now.
// For more details, see GlobalValue::mayBeDerefined.
if (!F->hasExactDefinition())
return false;
// We annotate nonnull return values, which are only applicable to
// pointer types.
if (!F->getReturnType()->isPointerTy())
continue;
bool Speculative = false;
if (isReturnNonNull(F, SCCNodes, Speculative)) {
if (!Speculative) {
// Mark the function eagerly since we may discover a function
// which prevents us from speculating about the entire SCC
LLVM_DEBUG(dbgs() << "Eagerly marking " << F->getName()
<< " as nonnull\n");
F->addAttribute(AttributeList::ReturnIndex, Attribute::NonNull);
++NumNonNullReturn;
MadeChange = true;
}
continue;
}
// At least one function returns something which could be null, can't
// speculate any more.
SCCReturnsNonNull = false;
}
if (SCCReturnsNonNull) {
for (Function *F : SCCNodes) {
if (F->getAttributes().hasAttribute(AttributeList::ReturnIndex,
Attribute::NonNull) ||
!F->getReturnType()->isPointerTy())
continue;
LLVM_DEBUG(dbgs() << "SCC marking " << F->getName() << " as nonnull\n");
F->addAttribute(AttributeList::ReturnIndex, Attribute::NonNull);
++NumNonNullReturn;
MadeChange = true;
}
}
return MadeChange;
}
namespace {
/// Collects a set of attribute inference requests and performs them all in one
/// go on a single SCC Node. Inference involves scanning function bodies
/// looking for instructions that violate attribute assumptions.
/// As soon as all the bodies are fine we are free to set the attribute.
/// Customization of inference for individual attributes is performed by
/// providing a handful of predicates for each attribute.
class AttributeInferer {
public:
/// Describes a request for inference of a single attribute.
struct InferenceDescriptor {
/// Returns true if this function does not have to be handled.
/// General intent for this predicate is to provide an optimization
/// for functions that do not need this attribute inference at all
/// (say, for functions that already have the attribute).
std::function<bool(const Function &)> SkipFunction;
/// Returns true if this instruction violates attribute assumptions.
std::function<bool(Instruction &)> InstrBreaksAttribute;
/// Sets the inferred attribute for this function.
std::function<void(Function &)> SetAttribute;
/// Attribute we derive.
Attribute::AttrKind AKind;
/// If true, only "exact" definitions can be used to infer this attribute.
/// See GlobalValue::isDefinitionExact.
bool RequiresExactDefinition;
InferenceDescriptor(Attribute::AttrKind AK,
std::function<bool(const Function &)> SkipFunc,
std::function<bool(Instruction &)> InstrScan,
std::function<void(Function &)> SetAttr,
bool ReqExactDef)
: SkipFunction(SkipFunc), InstrBreaksAttribute(InstrScan),
SetAttribute(SetAttr), AKind(AK),
RequiresExactDefinition(ReqExactDef) {}
};
private:
SmallVector<InferenceDescriptor, 4> InferenceDescriptors;
public:
void registerAttrInference(InferenceDescriptor AttrInference) {
InferenceDescriptors.push_back(AttrInference);
}
bool run(const SCCNodeSet &SCCNodes);
};
/// Perform all the requested attribute inference actions according to the
/// attribute predicates stored before.
bool AttributeInferer::run(const SCCNodeSet &SCCNodes) {
SmallVector<InferenceDescriptor, 4> InferInSCC = InferenceDescriptors;
// Go through all the functions in SCC and check corresponding attribute
// assumptions for each of them. Attributes that are invalid for this SCC
// will be removed from InferInSCC.
for (Function *F : SCCNodes) {
// No attributes whose assumptions are still valid - done.
if (InferInSCC.empty())
return false;
// Check if our attributes ever need scanning/can be scanned.
llvm::erase_if(InferInSCC, [F](const InferenceDescriptor &ID) {
if (ID.SkipFunction(*F))
return false;
// Remove from further inference (invalidate) when visiting a function
// that has no instructions to scan/has an unsuitable definition.
return F->isDeclaration() ||
(ID.RequiresExactDefinition && !F->hasExactDefinition());
});
// For each attribute still in InferInSCC that doesn't explicitly skip F,
// set up the F instructions scan to verify assumptions of the attribute.
SmallVector<InferenceDescriptor, 4> InferInThisFunc;
llvm::copy_if(
InferInSCC, std::back_inserter(InferInThisFunc),
[F](const InferenceDescriptor &ID) { return !ID.SkipFunction(*F); });
if (InferInThisFunc.empty())
continue;
// Start instruction scan.
for (Instruction &I : instructions(*F)) {
llvm::erase_if(InferInThisFunc, [&](const InferenceDescriptor &ID) {
if (!ID.InstrBreaksAttribute(I))
return false;
// Remove attribute from further inference on any other functions
// because attribute assumptions have just been violated.
llvm::erase_if(InferInSCC, [&ID](const InferenceDescriptor &D) {
return D.AKind == ID.AKind;
});
// Remove attribute from the rest of current instruction scan.
return true;
});
if (InferInThisFunc.empty())
break;
}
}
if (InferInSCC.empty())
return false;
bool Changed = false;
for (Function *F : SCCNodes)
// At this point InferInSCC contains only functions that were either:
// - explicitly skipped from scan/inference, or
// - verified to have no instructions that break attribute assumptions.
// Hence we just go and force the attribute for all non-skipped functions.
for (auto &ID : InferInSCC) {
if (ID.SkipFunction(*F))
continue;
Changed = true;
ID.SetAttribute(*F);
}
return Changed;
}
} // end anonymous namespace
/// Helper for non-Convergent inference predicate InstrBreaksAttribute.
static bool InstrBreaksNonConvergent(Instruction &I,
const SCCNodeSet &SCCNodes) {
const CallSite CS(&I);
// Breaks non-convergent assumption if CS is a convergent call to a function
// not in the SCC.
return CS && CS.isConvergent() && SCCNodes.count(CS.getCalledFunction()) == 0;
}
/// Helper for NoUnwind inference predicate InstrBreaksAttribute.
static bool InstrBreaksNonThrowing(Instruction &I, const SCCNodeSet &SCCNodes) {
if (!I.mayThrow())
return false;
if (const auto *CI = dyn_cast<CallInst>(&I)) {
if (Function *Callee = CI->getCalledFunction()) {
// I is a may-throw call to a function inside our SCC. This doesn't
// invalidate our current working assumption that the SCC is no-throw; we
// just have to scan that other function.
if (SCCNodes.count(Callee) > 0)
return false;
}
}
return true;
}
/// Helper for NoFree inference predicate InstrBreaksAttribute.
static bool InstrBreaksNoFree(Instruction &I, const SCCNodeSet &SCCNodes) {
CallSite CS(&I);
if (!CS)
return false;
Function *Callee = CS.getCalledFunction();
if (!Callee)
return true;
if (Callee->doesNotFreeMemory())
return false;
if (SCCNodes.count(Callee) > 0)
return false;
return true;
}
/// Infer attributes from all functions in the SCC by scanning every
/// instruction for compliance to the attribute assumptions. Currently it
/// does:
/// - removal of Convergent attribute
/// - addition of NoUnwind attribute
///
/// Returns true if any changes to function attributes were made.
static bool inferAttrsFromFunctionBodies(const SCCNodeSet &SCCNodes) {
AttributeInferer AI;
// Request to remove the convergent attribute from all functions in the SCC
// if every callsite within the SCC is not convergent (except for calls
// to functions within the SCC).
// Note: Removal of the attr from the callsites will happen in
// InstCombineCalls separately.
AI.registerAttrInference(AttributeInferer::InferenceDescriptor{
Attribute::Convergent,
// Skip non-convergent functions.
[](const Function &F) { return !F.isConvergent(); },
// Instructions that break non-convergent assumption.
[SCCNodes](Instruction &I) {
return InstrBreaksNonConvergent(I, SCCNodes);
},
[](Function &F) {
LLVM_DEBUG(dbgs() << "Removing convergent attr from fn " << F.getName()
<< "\n");
F.setNotConvergent();
},
/* RequiresExactDefinition= */ false});
if (!DisableNoUnwindInference)
// Request to infer nounwind attribute for all the functions in the SCC if
// every callsite within the SCC is not throwing (except for calls to
// functions within the SCC). Note that nounwind attribute suffers from
// derefinement - results may change depending on how functions are
// optimized. Thus it can be inferred only from exact definitions.
AI.registerAttrInference(AttributeInferer::InferenceDescriptor{
Attribute::NoUnwind,
// Skip non-throwing functions.
[](const Function &F) { return F.doesNotThrow(); },
// Instructions that break non-throwing assumption.
[SCCNodes](Instruction &I) {
return InstrBreaksNonThrowing(I, SCCNodes);
},
[](Function &F) {
LLVM_DEBUG(dbgs()
<< "Adding nounwind attr to fn " << F.getName() << "\n");
F.setDoesNotThrow();
++NumNoUnwind;
},
/* RequiresExactDefinition= */ true});
if (!DisableNoFreeInference)
// Request to infer nofree attribute for all the functions in the SCC if
// every callsite within the SCC does not directly or indirectly free
// memory (except for calls to functions within the SCC). Note that nofree
// attribute suffers from derefinement - results may change depending on
// how functions are optimized. Thus it can be inferred only from exact
// definitions.
AI.registerAttrInference(AttributeInferer::InferenceDescriptor{
Attribute::NoFree,
// Skip functions known not to free memory.
[](const Function &F) { return F.doesNotFreeMemory(); },
// Instructions that break non-deallocating assumption.
[SCCNodes](Instruction &I) {
return InstrBreaksNoFree(I, SCCNodes);
},
[](Function &F) {
LLVM_DEBUG(dbgs()
<< "Adding nofree attr to fn " << F.getName() << "\n");
F.setDoesNotFreeMemory();
++NumNoFree;
},
/* RequiresExactDefinition= */ true});
// Perform all the requested attribute inference actions.
return AI.run(SCCNodes);
}
static bool setDoesNotRecurse(Function &F) {
if (F.doesNotRecurse())
return false;
F.setDoesNotRecurse();
++NumNoRecurse;
return true;
}
static bool addNoRecurseAttrs(const SCCNodeSet &SCCNodes) {
// Try and identify functions that do not recurse.
// If the SCC contains multiple nodes we know for sure there is recursion.
if (SCCNodes.size() != 1)
return false;
Function *F = *SCCNodes.begin();
if (!F || !F->hasExactDefinition() || F->doesNotRecurse())
return false;
// If all of the calls in F are identifiable and are to norecurse functions, F
// is norecurse. This check also detects self-recursion as F is not currently
// marked norecurse, so any called from F to F will not be marked norecurse.
for (auto &BB : *F)
for (auto &I : BB.instructionsWithoutDebug())
if (auto CS = CallSite(&I)) {
Function *Callee = CS.getCalledFunction();
if (!Callee || Callee == F || !Callee->doesNotRecurse())
// Function calls a potentially recursive function.
return false;
}
// Every call was to a non-recursive function other than this function, and
// we have no indirect recursion as the SCC size is one. This function cannot
// recurse.
return setDoesNotRecurse(*F);
}
template <typename AARGetterT>
static bool deriveAttrsInPostOrder(SCCNodeSet &SCCNodes,
AARGetterT &&AARGetter,
bool HasUnknownCall) {
bool Changed = false;
// Bail if the SCC only contains optnone functions.
if (SCCNodes.empty())
return Changed;
Changed |= addArgumentReturnedAttrs(SCCNodes);
Changed |= addReadAttrs(SCCNodes, AARGetter);
Changed |= addArgumentAttrs(SCCNodes);
// If we have no external nodes participating in the SCC, we can deduce some
// more precise attributes as well.
if (!HasUnknownCall) {
Changed |= addNoAliasAttrs(SCCNodes);
Changed |= addNonNullAttrs(SCCNodes);
Changed |= inferAttrsFromFunctionBodies(SCCNodes);
Changed |= addNoRecurseAttrs(SCCNodes);
}
return Changed;
}
PreservedAnalyses PostOrderFunctionAttrsPass::run(LazyCallGraph::SCC &C,
CGSCCAnalysisManager &AM,
LazyCallGraph &CG,
CGSCCUpdateResult &) {
FunctionAnalysisManager &FAM =
AM.getResult<FunctionAnalysisManagerCGSCCProxy>(C, CG).getManager();
// We pass a lambda into functions to wire them up to the analysis manager
// for getting function analyses.
auto AARGetter = [&](Function &F) -> AAResults & {
return FAM.getResult<AAManager>(F);
};
// Fill SCCNodes with the elements of the SCC. Also track whether there are
// any external or opt-none nodes that will prevent us from optimizing any
// part of the SCC.
SCCNodeSet SCCNodes;
bool HasUnknownCall = false;
for (LazyCallGraph::Node &N : C) {
Function &F = N.getFunction();
if (F.hasOptNone() || F.hasFnAttribute(Attribute::Naked)) {
// Treat any function we're trying not to optimize as if it were an
// indirect call and omit it from the node set used below.
HasUnknownCall = true;
continue;
}
// Track whether any functions in this SCC have an unknown call edge.
// Note: if this is ever a performance hit, we can common it with
// subsequent routines which also do scans over the instructions of the
// function.
if (!HasUnknownCall)
for (Instruction &I : instructions(F))
if (auto CS = CallSite(&I))
if (!CS.getCalledFunction()) {
HasUnknownCall = true;
break;
}
SCCNodes.insert(&F);
}
if (deriveAttrsInPostOrder(SCCNodes, AARGetter, HasUnknownCall))
return PreservedAnalyses::none();
return PreservedAnalyses::all();
}
namespace {
struct PostOrderFunctionAttrsLegacyPass : public CallGraphSCCPass {
// Pass identification, replacement for typeid
static char ID;
PostOrderFunctionAttrsLegacyPass() : CallGraphSCCPass(ID) {
initializePostOrderFunctionAttrsLegacyPassPass(
*PassRegistry::getPassRegistry());
}
bool runOnSCC(CallGraphSCC &SCC) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
AU.addRequired<AssumptionCacheTracker>();
getAAResultsAnalysisUsage(AU);
CallGraphSCCPass::getAnalysisUsage(AU);
}
};
} // end anonymous namespace
char PostOrderFunctionAttrsLegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(PostOrderFunctionAttrsLegacyPass, "functionattrs",
"Deduce function attributes", false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
INITIALIZE_PASS_END(PostOrderFunctionAttrsLegacyPass, "functionattrs",
"Deduce function attributes", false, false)
Pass *llvm::createPostOrderFunctionAttrsLegacyPass() {
return new PostOrderFunctionAttrsLegacyPass();
}
template <typename AARGetterT>
static bool runImpl(CallGraphSCC &SCC, AARGetterT AARGetter) {
// Fill SCCNodes with the elements of the SCC. Used for quickly looking up
// whether a given CallGraphNode is in this SCC. Also track whether there are
// any external or opt-none nodes that will prevent us from optimizing any
// part of the SCC.
SCCNodeSet SCCNodes;
bool ExternalNode = false;
for (CallGraphNode *I : SCC) {
Function *F = I->getFunction();
if (!F || F->hasOptNone() || F->hasFnAttribute(Attribute::Naked)) {
// External node or function we're trying not to optimize - we both avoid
// transform them and avoid leveraging information they provide.
ExternalNode = true;
continue;
}
SCCNodes.insert(F);
}
return deriveAttrsInPostOrder(SCCNodes, AARGetter, ExternalNode);
}
bool PostOrderFunctionAttrsLegacyPass::runOnSCC(CallGraphSCC &SCC) {
if (skipSCC(SCC))
return false;
return runImpl(SCC, LegacyAARGetter(*this));
}
namespace {
struct ReversePostOrderFunctionAttrsLegacyPass : public ModulePass {
// Pass identification, replacement for typeid
static char ID;
ReversePostOrderFunctionAttrsLegacyPass() : ModulePass(ID) {
initializeReversePostOrderFunctionAttrsLegacyPassPass(
*PassRegistry::getPassRegistry());
}
bool runOnModule(Module &M) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
AU.addRequired<CallGraphWrapperPass>();
AU.addPreserved<CallGraphWrapperPass>();
}
};
} // end anonymous namespace
char ReversePostOrderFunctionAttrsLegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(ReversePostOrderFunctionAttrsLegacyPass, "rpo-functionattrs",
"Deduce function attributes in RPO", false, false)
INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
INITIALIZE_PASS_END(ReversePostOrderFunctionAttrsLegacyPass, "rpo-functionattrs",
"Deduce function attributes in RPO", false, false)
Pass *llvm::createReversePostOrderFunctionAttrsPass() {
return new ReversePostOrderFunctionAttrsLegacyPass();
}
static bool addNoRecurseAttrsTopDown(Function &F) {
// We check the preconditions for the function prior to calling this to avoid
// the cost of building up a reversible post-order list. We assert them here
// to make sure none of the invariants this relies on were violated.
assert(!F.isDeclaration() && "Cannot deduce norecurse without a definition!");
assert(!F.doesNotRecurse() &&
"This function has already been deduced as norecurs!");
assert(F.hasInternalLinkage() &&
"Can only do top-down deduction for internal linkage functions!");
// If F is internal and all of its uses are calls from a non-recursive
// functions, then none of its calls could in fact recurse without going
// through a function marked norecurse, and so we can mark this function too
// as norecurse. Note that the uses must actually be calls -- otherwise
// a pointer to this function could be returned from a norecurse function but
// this function could be recursively (indirectly) called. Note that this
// also detects if F is directly recursive as F is not yet marked as
// a norecurse function.
for (auto *U : F.users()) {
auto *I = dyn_cast<Instruction>(U);
if (!I)
return false;
CallSite CS(I);
if (!CS || !CS.getParent()->getParent()->doesNotRecurse())
return false;
}
return setDoesNotRecurse(F);
}
static bool deduceFunctionAttributeInRPO(Module &M, CallGraph &CG) {
// We only have a post-order SCC traversal (because SCCs are inherently
// discovered in post-order), so we accumulate them in a vector and then walk
// it in reverse. This is simpler than using the RPO iterator infrastructure
// because we need to combine SCC detection and the PO walk of the call
// graph. We can also cheat egregiously because we're primarily interested in
// synthesizing norecurse and so we can only save the singular SCCs as SCCs
// with multiple functions in them will clearly be recursive.
SmallVector<Function *, 16> Worklist;
for (scc_iterator<CallGraph *> I = scc_begin(&CG); !I.isAtEnd(); ++I) {
if (I->size() != 1)
continue;
Function *F = I->front()->getFunction();
if (F && !F->isDeclaration() && !F->doesNotRecurse() &&
F->hasInternalLinkage())
Worklist.push_back(F);
}
bool Changed = false;
for (auto *F : llvm::reverse(Worklist))
Changed |= addNoRecurseAttrsTopDown(*F);
return Changed;
}
bool ReversePostOrderFunctionAttrsLegacyPass::runOnModule(Module &M) {
if (skipModule(M))
return false;
auto &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
return deduceFunctionAttributeInRPO(M, CG);
}
PreservedAnalyses
ReversePostOrderFunctionAttrsPass::run(Module &M, ModuleAnalysisManager &AM) {
auto &CG = AM.getResult<CallGraphAnalysis>(M);
if (!deduceFunctionAttributeInRPO(M, CG))
return PreservedAnalyses::all();
PreservedAnalyses PA;
PA.preserve<CallGraphAnalysis>();
return PA;
}
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